Syrian state TV also reported the blast, calling it a "terrorist" attack by a suicide bomber on a heavily populated area.

The pro-regime TV station Al-Ikhbariya showed images of what appeared to be at least four dead bodies on the ground and cars on fire. The footage shows firefighters trying to douse cars on fire and lifeless bodies lying on the grass of a public garden.

Eyewitnesses at the scene said a car had exploded at a security checkpoint between the Russian Embassy and the central headquarters of the ruling Baath party of President Bashar Assad.

Ambulances rushed to the scene of the blast, which also shattered windows and sent up a huge cloud of smoke visible throughout much of the city, eyewitnesses said.

"It was huge, everything in the shop turned upside down," one local resident said, speaking on condition of anonymity for fear of retribution for speaking with foreign media.

Damascus has so far mostly avoided the large-scale violence that has destroyed other Syrian cities, though deadly car bombings have targeted government buildings in the capital.

The blast followed two mortar attacks in as many days on the capital. On Wednesday, two mortar shells exploded near a soccer stadium in Damascus, killing one player. The day before, two mortar shells went off near one of Assad's three palaces in the city, causing only material damage.

Not long after the first blast Thursday, a security official reported a second blast in the capital's northeastern Barzeh neighborhood. He had no other information and spoke on condition of anonymity because he was not authorized to brief the media.

Syria's conflict began in March 2011 with political protests against the government and has since evolved into a civil war between Assad's regime and hundreds of rebel groups seeking to topple it. The U.N. says some 70,000 people have been killed in the conflict so far.